1. Field of the Invention
The present invention relates to a coating method and a coating system and, more particularly, to a coating method and a coating system for coating a member, being conveyed, with a coating gun reciprocating in a predetermined direction.
2. Description of the Related Art
It is known that the member being conveyed is coated with a coating gun which reciprocates in a predetermined direction, i.e. in the direction perpendicular to the direction of conveyance of the member to be coated.
For example, when a side portion of the body of an automotive vehicle conveyed into the coating station in a coating line is coated, the coating gun usually reciprocates in a vertical direction with respect to the side portion of the body.
For example Japanese Patent Laid-open Publication (kokai) 1-297,168 discloses a coating method and a coating system. In this prior technology, the side portion of the body is divided into plural sections in the vertical direction and the coating guns are disposed so as to correspond to the plural sections of the side portion. Each of the coating guns is arranged to reciprocate in a vertical direction within the length defined by the divided sections of the side portion of the body, thereby reducing the amount of displacement of each of the coating guns to a considerable extent and speeding up the coating operation in the coating line with improved efficiency in the coating operation.
It can be noted, however, that the prior technology requires a plurality of the coating guns and that the displacement or movement of the coating gun and the operation of spraying a paint should be separately controlled. Thus, the prior technology suffers from the disadvantages that the system itself becomes larger in size and the structure and configuration of the coating system becomes more complex so that a wide space for installation is required and costs of equipment become more expensive.
On the other hand, Japanese Utility Model Laid-open Publication (kokai) No. 62-151,970 proposes a compact system that requires only one coating gun for coating a whole side portion of the body. In this system, a guide rail is disposed so as to guide the coating gun vertically along and parallel to a curved shape of the side portion of the body. Further, this is provided with a tilt mechanism at a portion supporting the coating gun so as to tilt the coating gun at a given angle of spraying a paint toward the curved side of the member in a distance away from the surface of the curved side portion.
It is to be noted, however, that when the paint is sprayed with a spraying gun, the thickness of a coat formed by one spraying operation on the surface of the member to be coated is not constant in the widthwise direction of a sectional pattern of the coat. Specifically, the middle portion of the sectional pattern becomes thicker than both side portions.
Thus, in order to provide a coating with a uniform coat thickness and of Good quality, it is desired that a distance between two passes, that is, a pass pitch, be restricted to a value smaller than a predetermined value with respect to the width of the pattern and that the paint is coated with one pattern of a coat overlapping partially with the pattern of another coat that follows.
In other words, it is desired to ensure a constant number of applications of the paint to the side portion of the member to be coated and to hold the number of applications constant over the entire area of the surface of the member to be coated.
It can be noted that the side portion of the body is composed of side panels which are different in vertical height. More specifically, the side portion of the body comprises a front portion (a front fender side section), a middle portion (a compartment side section), and a rear portion (a rear fender side section), and these three side panel sections have different vertical lengths.
When the side portion consisting of those different side panel sections is coated with one coating or spraying gun, a conventional technique is such that a reciprocating stroke of the coating gun is held constant, regardless of the different vertical lengths among the side sections of the vehicle. Specifically, the reciprocating stroke of the coating gun is adapted to the vertically longest compartment side section and the paint is coated on the compartment side section and the spraying of the paint is partially ceased, while the stroke operation only is still in process, thereby failing to coat the portions before and behind the compartment side section as well as above the front and rear fender side sections. Alternatively, the reciprocating stroke of the coating gun is adapted to either of the front fender side section or the rear fender side section and the portions outside the reach of the reciprocating stroke of the coating gun are coated separately.
It can be noted, however, that the former carries out the stroke operation at the portions where no paint is sprayed, on the one hand, thereby reducing the efficiency in the coating operation, and that the latter requires a separate coating process for the portions outside the reach of the reciprocating stroke of the coating gun, on the other hand, thereby impairing improvements in production.